The present invention relates generally to silicon-based structures and in particular, to a room-temperature, electrically tunable electromagnetic bandgap (“TEBG”) structure using a ferroelectric thin film on a semiconductor substrate, tunable devices that include such a TEBG structure, such as a monolithic microwave integrated circuit (“MMIC”), and a method producing such a TEBG structure.
Prior art electromagnetic bandgap (“EBG”) structures are essentially one-, two-, and three-dimensional metal-dielectric and dielectric—dielectric periodic structures. EBG structures, known also as photonic bandgap (“PBG”) crystals, are extensively considered for applications in microwave devices, including filters, multiplexers, phase shifters, and frequency selective surfaces (“FSS”). In EBG structures, electromagnetic waves experience frequency bands, where they cannot propagate, a feature similar to wave (electron, electromagnetic) propagation in physical crystals considered in solid-state physics. These frequency bands are similar to forbidden energy bands in semiconductors.
Prior art EBG structures also exhibit unexpected properties. For example, they may form a “conducting magnetic wall,” i.e., a conducting wall where the tangential component of the electric field is rather high, like on the surface of a dielectric. For this reason EBG structures can be used to suppress surface waves in antennas, and substrates in microstrip/coplanar waveguides. Two-dimensional (“2D”) EBG crystals in FSS consist of periodic arrays of metallic patch resonators acting as special filters for electromagnetic waves, exhibiting frequency stop bands near resonance of the patches. These filters are used in radomes, in polarization converters, and a number of other military applications. One of the main advantages of EBG structures is their simplicity, and compatibility with printed circuit board (“PCB”) technology, making them rather cost effective.
The main disadvantage of prior art EBG structures is their large size (e.g., greater than 3 centimeters) at low microwave frequencies, since the periodicity of the structure is proportional to the wavelength of microwave signal. This makes the applications of EBG structures at lower microwave frequencies (i.e., below 10 GHz) not practical. However, the frequency band 0.5–5.0 GHz is extensively used in microwave (mobile telephony) communications systems, and the frequency band 5.0–10 GHz is being considered for future advanced mobile telephony systems.